Blood clotting

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Blood is fluid in nature and is essential for the transport of nutrients including oxygen round the body through the circulatory system by the aid of the heart and blood vessels. The rupture of these blood vessels can be catastrophic and the body naturally solves this by the process of Hemostasis. Hemostasis helps prevent blood loss by three main stages namely[1]:

  1. Vasoconstriction
  2. Platelet Aggregation
  3. Coagulation

Contents

Vasoconstiction

The blood pressure in the damaged blood vessel decreases when vasoconstrictive paracrines released by the endothelium causes the constriction of the damaged blood vessel

Platelet Aggregation

Normally, the endothelium of blood vessels shield the circulating blood from the collagen matrix but when the vessel is damaged, the collagen matrix is exposed. This results in the interaction of platelet with the exposed collagen. The adhesion of a platelet with collagen initiates a positive feedback mechanism where signalling molecules released by activated platelet recruit other platelet molecules promoting platelet aggregation that forms a loose platelet plug in the hole[2].

During day-to-day life platelet aggregation could be very harmful and therefore the epithelial cells of our blood vessels (the Tunica intima) produces a protein called prostacyclin which prevents undesired platelet aggregation.

Coagulation

Coagulation is the process where blood looses its fluidity externally while still maintaining constant flow in the blood vessels. A series of steps leading to the formation of fibrin protein fibre involving different clotting factors. There are about thirteen known clotting factors:

These factors interact together to bring about coagulation cascade. These clotting factors are in an inactive state and must be activated to bring about blood clotting. Generally, the three stages involved in clotting formation are: formation of prothrombin activator, conversion of prothrombin into thrombin and finally thrombin is converted to fibrin[3].

It is this fibrin produced that stabilizes the platelet plug which is called 'clot'.

Upon repair of the vessel, the clot is eliminated and digested by an enzyme called plasmin.

It is very important that the body regulates hemostasis properly as it can lead to thrombosis wherein excess and haemorrhage where there is little hemostasis.

References

  1. Silverton D. (2010)Human Physiology; An Integrated Approach, 5th Edition, San Francisco; Pearson Education, Inc.
  2. Baron, W.F. and Boulpaep, E.L.,(2009) Medical Physiology: A Cellular and Molecular Approach,2nd Edition, Philadelphia; SAUNDERS ELSEVIER
  3. SEMBULINGAN K. AND SEMBULINGAN P.,(2003), ESSENTIALS OF MEDICAL PHYSIOLOGY 4th EDITION. NEW DELHI: JAYPEE BROTHERS MEDICAL PUBLISHERS.
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